The aim of the proposed research is to gain a better understanding of the regulatory mechanism in muscle. It is known that the contraction relaxation cycle of muscle is governed by the intracellular concentration of Ca2 ions. The mechanism whereby the contractile proteins recognize and translate the changes in Ca2 ion concentration is the theme of this proposal. Two muscle types will be studied; the first is skeletal muscle. A considerable amount of data has been accumulated with this tissue, and a reasonable theory, or model, has been put forward which accounts for many of the known facts. A key feature of the theory is the role of tropomyosin, which is thought to block reversibly the myosin-actin interaction. We intend to test this hypothesis by studying the function and biological activity of tropomyosin. We will also try to define the tropomyosin-actin and trypomyosin-troponin binding sites. Since the regulatory mechanism is sensitive to Ca2 ion we must consider the chemistry of troponin. In particular we are concerned with the "recognition phase." How does troponin know when the intracellular Ca2 ion concentration is at the contraction or relaxation level? Therefore we will study the chemistry of troponin C (the Ca2 ion binding component) in an attempt to determine what signal the Ca2 ion receptor passes on to the other protein components which are involved in the regulatory mechanism. One technique which will be used to investigate the conformation of TpC as a function of Ca2 ion concentration is nuclear magnetic resonance. The second muscle type is smooth muscle, and we will use both gizzard and vascular tissues as sources. In smooth muscle there is very little known about the biochemistry of the contractile proteins, and our intent is to characterize the components of the regulatory system and thus establish a molecular basis for future models. We will concentrate on the troponin analog of smooth muscle, although in order to gain a broader understanding of the mechanism it will be necessary to study the other proteins of the system, in particular myosin and trpomyosin.